There are two other places in Bohemia where ice is found in summer. One is on the Steinberg, in the county of Konaged;[132] it is a small basin, surrounded by trees, where, in the middle of summer, lumps of ice are found under basaltic debris. This ice is only formed, according to Sommer, in the hottest part of the year. The other is on the Zinkenstein, one of the highest points of the Vierzehnberg, in the circle of Leitmeritz. It is described by Sommer[133] as a cleft, five fathoms deep, in the basaltic rock, where ice is found in the hottest seasons. Professor Pleischl put this assertion to the test by visiting the spot in the end of August, when he found no signs of ice.

Another writer in Poggendorff[134] describes a somewhat similar appearance on the Saalberg. Here ice is found on the surface from June to the middle of August; and that, too, with a west exposure and in moderate shade. In July, the ice was so abundant that it could be seen from some distance: it was half a foot thick, and yielded neither to sun nor rain. In the middle of August there was no ice on the surface; but when the loose debris was removed, the most beautiful ice appeared, and at a little depth all was frozen as hard as if it had been the depth of winter.[135] The people who work in the neighbourhood declare that the place remains open, and free from ice or snow, in the greatest cold, and that no ice begins to form till the month of June. When the writer of the account in Poggendorff visited the ice-hole, the peasants were in the habit of carrying large masses of ice down to their houses, through a temperature of 81 deg. F.

Reich[136] gives a detailed and valuable account of the prevalence of subterranean ice on the Sauberg, a hill which forms one side of a ravine near Ehrenfriedersdorf. The surface is about 2,000 feet above the sea, and its mean temperature, as determined by many careful observations, about 45 deg. F. There are several tin-mines in this district, and the extended observations made by the authorities establish the curious fact that the mean temperature is considerably lower beneath than at the surface. For instance, in the S. Christoph pit, it is found that the mean temperature, at 15 fathoms below the surface, is only slightly above 42 deg. F.; while at the Morgenroether cross-cut the same mean temperature is found at a depth of 46 fathoms. The annual change of temperature is very small in these mines, and the maximum and minimum are reached very late; so that, if a point could be found with a mean temperature of 32 deg. F., ice would increase there up to June or even July, and then diminish until December or January; in which case the phenomenon so often said to be observed in connection with subterranean ice—the melting in winter and forming in summer—would really be presented.

The ice on the Sauberg is frequently found to commence at a depth of 3 or 4 fathoms, and in the years 1811 and 1813 it extended to 24 fathoms below the surface: this depth, however, was exceptionally great, and as a rule the limit is reached at about 14 fathoms.[137] The ice is usually not very firm, and can be broken by stout blows with a stick; but between the years 1790 and 1800, when it was found at a depth of from 3 to 9 fathoms, it was so hard that blasting became necessary, and at that time the miners were with difficulty protected from the effects of the severe cold. The greatest quantity of ice is found in the interstices of the rubbish-beds of old workings, and here it assumes a crystalline form, the rocks being covered with a 'fibrous' structure, arranged perpendicularly to their surface.

Reich reports the universal presence of cold currents of air in these shafts and mines, and, in consequence, takes the opportunity of contradicting a statement in Horner's Physik. Woerterbuch,[138] that the absence of all current of air is essential to the formation of subterranean ice. He quotes the case of the cheese-caves of Roquefort as a further confirmation of his own observations with regard to the connection between ice in caves and cold currents of air; but of the many accounts which I have met with of the curious caves referred to, both in books and from the lips of those who have visited them, not one has made any mention of ice.[139] He states, too, that when the strength of the current is diminished, its temperature is increased; a fact which all observations of the cold currents in caves, especially those made with so much care by M. Saussure, abundantly establish.

In the way of explanation, Reich mentions the possibility of rocks of peculiar formation possessing actually a low degree of temperature;[140] but he rejects this suggestion, preferring to believe that in some cases the cold resulting from evaporation is the cause of ice, and in others the greater specific gravity of cold as compared with warmer air.

In the Bulletin des Sciences Naturelles,[141] it is stated that a large quantity of ice is found in one of the recesses of the grotto of Antiparos—a fact which I have not seen mentioned elsewhere. After penetrating a long way through difficult fissures, a square chamber is at length reached, measuring 300 feet in length and breadth, with a height of about 80 feet. The walls and roof and floor are beautifully decorated with ice, and reflect all the colours of the rainbow. There are groups of pyramidal and round columns, and in some parts of the cave screens or curtains of ice 10 or 12 feet broad hang down to the floor.

In a later volume of the same periodical,[142] there is a description of a hill in Virginia where ice is found in summer. This hill lies near the road between Winchester and Romney, on the North River, latitude 39 N. One side of the hill is entirely composed of loose stones from ten to twenty pounds in weight, and under these the ice is found, although their upper surface is exposed to the full sun from 9 or 10 A.M. till sunset. In all seasons there is an abundance of ice. A writer in the 'London and Paris Observer'[143] visited the spot on the 4th of July, after a time of stifling heat, and in ten minutes he found more ice than the whole party could have carried away. He did not explore any farther than the foot of the hill; but the neighbours, who used the ice regularly in summer, assured him that it was to be found high up also. A constant and strong current issued from the crevices, stronger and infinitely colder than the current in the famous 'blowing cave' of Virginia. A man had built a store-room for meat within the influence of one of these currents, and hard dry icicles were seen hanging from the wooden supports inside: the flies, too, which had been attracted by the meat, were found frozen on to the stones. This is not the only district where ice is found within temperate latitudes in North America. In Professor Silliman's 'American Journal of Science,'[144] in a sketch of the geology of the township of Salisbury, Con. (latitude 43 deg. N.), 'natural ice-houses' are mentioned. These consist of chasms of considerable extent in the mica-state, where ice and snow remain during the greater part of the year. The principal of these chasms lies in the east part of the town, and is several hundred feet long, sixty feet deep, and about forty wide. The slate is of a very compact kind; and the walls are perpendicular, and correspond with much exactness. At the bottom is a cold spring, and a cave of considerable extent, in which it is probable that the ice lies—for the writer does not specify the position in which it is found. The chasm is a favourite retreat in summer, and is called the Wolf-hollow, from its having formerly been a famous haunt for wolves.

Similar receptacles for summer-ice are found in several places in North America. In the forty-ninth volume of the Sitzungsberichte der Kaiserl. Akademie in Wien (1te. Abth.), a list of references to various ice-holes is appended to a paper by Dr. Boue on the geology of Servia. Many of the passages referred to have nothing to do with ice-caves, as, for instance, the sections of De Saussure's book describing his observations of 'cold caves', or the account of the mass of ice and snow from which the river Jumna springs, for which Dr. Boue refers to the 'Philosophical Magazine' for November 1823, meaning, in fact, the 'London Magazine'. The 'Description des Glacieres' of M. Bourrit is also given as a part of the literature on ice-caves; whereas (see the account of the Glaciere of Montarquis, in the Valley of Reposoir) by 'glaciere' M. Bourrit meant only a locality where ice is to be found, or a glacier district. Dr. Boue, however, gives some references to the 'American Journal of Science' which it is possible to make out by a careful search in the neighbourhood of the volume and page he mentions. In vol. iv. (1822,—Dr. Boue says 1821) there is an account by the editor[145] of a natural ice-house in the township of Meriden, Con., between Hartford and Newhaven, at an elevation of not more than 200 feet above the level of the sea. The ice is found in a narrow defile, which is hemmed in by perpendicular sides of trap-rock, and displays a perfect chaos of fallen blocks of stone. The defile is so narrow, that the sun's rays only reach it for an hour in the course of the day; and even the trees and rocks, and beds of leaves, protect the ice from any very material damage. Dr. Silliman visited this defile on the 23rd July, 1821,[146] with Dr. Isaac Hough, the keeper of a neighbouring inn, and found that the ice was only partially visible, in consequence of the large collection of leaves which lay on it: they sent a boy down with a hatchet, and he brought up some large firm masses, one of which, weighing several pounds, they carried twenty miles to Newhaven, where it did not entirely disappear till the morning of the third day. Seven miles from Newhaven, in the township of Branford, there is a similar collection of ice. In both of these cases, the ice is mixed with a considerable quantity of leaves and dirt.

In the same volume (p. 331,—Dr. Boue says p. 33), two accounts are given of a natural ice-house near the summit of a hill in the neighbourhood of Williamstown (Mass.). In the next volume there is a further account of it by Professor Dewey, stating that since the trees in the neighbourhood had been cut, the snow and ice had disappeared each year about the first of August.

In vol. xlvi. (p. 331) an ice mountain in Wallingford, Rutland County (Vt.), is described, which is ordinarily known in the neighbourhood as the ice-bed. An area of thirty or fifty acres of ground is covered with massive debris of grey quartz from the mountains which overhang it; and here—especially in a deep ravine into which many of the falling blocks of stone have penetrated—ice is found in large quantities. It appears to be formed during the melting of the snow in February, March, and April, and vanishes in the course of the summer, in hot years as early as the last days of June.

These descriptions call to mind the Glaciere of Arc-sous-Cicon, in which many of the features of the American ice-caves are reproduced. An American photograph is current in this country, in the form of a stereoscopic slide, representing an ice-cave in the White Mountains, New Hampshire; but it is only a winter cave, and in no way resembles any of the glacieres I have seen. It is merely a collection of long and slender icicles, with beds of ice formed upon stones and trunks of trees on the ground; nothing more, in fact, than is to be seen in any tolerably severe winter in the neighbourhood of a cascade in a sheltered Scotch burn.

The 'American Journal of Science' (xxxvi. 184) gives a curious instance of a freezing-well near the village of Owego, three-quarters of a mile from the Susquehanna river. The depth of the well is 77 feet, and for four or five months in the year the surface of the water is frozen so hard as to render the well useless. Large masses of ice have been found in it late in July. A thermometer, which stood at 68 deg. in the sun, fell to 30 deg. in fifteen minutes at the bottom of the well; and the men who made the well were forced to put on thick clothing in June, and even so could not work for more than two hours at a time. No other well in that neighbourhood presents the same phenomenon. A lighted candle was let down, and the flame became agitated and thrown in one direction at a depth of 30 feet, but was quite still at the bottom; where, however, it soon died out. The water is hard or limestone water.

Rocks of volcanic formation would seem to afford favourable opportunities for the formation of ice. Scrope mentions this fact in an account of the curious district called Eiffel or Eifel, in Rhenish Prussia, which was published originally in the 'Edinburgh Journal of Science,'[147] and has since been translated in Keferstein's Deutschland.[148] The village of Roth, near Andernach, is built on a current of basalt, derived from the cone above it, which has at some time sent down a stream of lava to the north and west. A small cavern near the village, forming the mouth of a deep fissure in the lava-stream, half-way up the cone, displays a phenomenon which the writer says he has often observed in volcanic formations. The floor of the cavern was covered with a crust of ice at the time of his visit, about noon on a very hot day in August. The peasants report that there is always ice in summer, and never in winter, when the sheep retreat to the cave on account of its warmth. Steininger[149] found a thickness of 3 feet of ice on September 19, 1818, but it was evidently in a melting state, and the thermometer stood at 36.5 F. in the cavern. He describes it as possessing a narrow entrance facing north, entirely sheltered from the sun by lava-rocks, and by the trees of a wood which covers the cone of scoria.

Scrope believes that this is the mouth of one of the arched galleries so frequently met with under lava in Iceland, Bourbon, and elsewhere; and on this he founds his explanation of the phenomenon. If the other extremity is connected with the external air at a much lower level, a current of air must be constantly driven up this gallery, and in its passage will be dried by the absorbent nature of the rock—which is perhaps partly owing to the sulphuric or muriatic acid it contains[150]—and the evaporation caused by this current produces a coating of ice on the floor of the grotto, where there is a superficial rill of water. The more rarified the lower external air, the more rapid will be the current of cool air; and, therefore, the greater the evaporation. The winter phenomenon is to be explained by the fact that the current of air will be about the mean annual temperature of the district, taking its temperature, in fact, from the rocks through which it passes; and, therefore, by contrast the grotto will appear warm.

The same writer mentions a similar example of summer ice in Auvergne.[151] There is a natural grotto in the basalt near Pont Gibaud, some miles to the north-west of Clermont, in which a small spring is found partly frozen during the greatest heats of summer, while the water is said to be warm in winter; probably, Scrope observes, only seeming to be warm by contrast with the external temperature. The water is apparently frozen by means of the powerful evaporation produced by a current of very dry air proceeding from some long fissures or arched galleries which communicate with the cave. In this case also the writer suggests that the air owes its dryness to the absorbent qualities of the lava through which it passes: he repeats, too, the remark that the phenomenon is of common occurrence in caverns in volcanic districts.[152]

There is a remarkable instance of ice occurring under lava, near the Casa Inglese on Mount Etna, which it may be as well to mention, though the causes of its existence have probably nothing in common with the phenomena of ice-caves, or summer ice. An account of it is to be found in Sir Charles Lyell's 'Elements of Geology.'[153] It appears that the summer and autumn of 1828 were so hot, that the artificial ice-houses of Catania and the adjoining parts of Sicily failed. Signer M. Gemmellaro had long believed that a small mass of perennial ice at the foot of the highest cone of Etna was only a part of a large and continuous glacier covered by a lava current, and from this he expected to derive an abundant supply of ice. He procured a large body of workmen, and quarried into the ice; but though he thus proved the superposition of lava for several hundred yards, the ice was so hard, and the expense of quarrying consequently so great, that the works were abandoned. This was on the south-east of the cone, not far from the Casa Inglese. Sir Charles Lyell suggests that, probably, at the commencement of some eruption, a large mass of snow has been thickly covered with volcanic sand, showered upon it before the arrival of the lava itself. This sand is a non-conductor of heat, and would therefore tend to preserve the snow from complete fusion when the hot lava-stream passed over it, and thus the existence of the underground glacier may be explained. The peasants of the district are so well acquainted with the non-conducting properties of volcanic sand, that they secure an annual store of snow, for providing water in summer, by strewing a layer of sand a few inches thick upon a field of snow, thus effectually shutting out the heat of the sun. It is curious that when De Saussure visited Chamouni for the first time, his attention was arrested by the sight of women sowing what seemed to be grain of some kind in the snow; but, on enquiring, he found that it was only black earth, which the inhabitants spread on the snow in spring, in order to make it disappear sooner. He was told that snow thus treated would melt a fortnight or three weeks before the ordinary time for its disappearance in the valley; but it will be seen that this does not contradict the theory of the Sicilian peasants.[154]

Sir Charles Lyell adds that, after what he saw on Mount Etna, he should not be surprised to find layers of glacier and lava alternating in some parts of Iceland.

Something similar was observed by Von Kotzebue, near the sound which bears his name.[155] His party was encamped on a large plain covered with moss and grass, when they discovered a fissure which revealed the fact that the moss and grass were but a thin coating on a layer of ice a hundred feet thick. This was not mere frozen ground, but aboriginal ice; for, in the ice which formed the walls of the fissure, they found the bones and teeth of mammoths embedded.

The frozen soil of Jakutsk, in Siberia, has for many years attracted considerable attention. The ordinary law of increase of temperature in descending below the surface of the earth would appear, however, to be only modified here; for it is found in sinking a well which has afforded opportunities for observing the state of the soil, that the temperature gradually increases with the depth.[156]

Two ice-caverns were examined by Georgi, in the course of his travels in Russia.[157] One occurs near the mines of Lurgikan, on the east side of a hill about 450 feet high, not far from the confluence of the Lurgikan stream with the Schilka (a tributary of the Amur), in the province of Nertschinsk. In the course of driving an adit in one of the lead-mines, in the year 1770, the workmen were struck by the hollow sound given forth by the rock, and, on investigation, they found an immense grotto or fissure, of which the entrance was so much blocked up by ice that they had much difficulty in sliding down by means of ropes. The fissure extended under the hill, in a direction from north to south, and was 130 fathoms long, from 1 to 8 broad, and from 3 to 12 high. Where it approached nearest the surface, the thickness of the roof was about 10 fathoms. The rock is described by Georgi as quarzig, braeunlich, und von einem starken Kalkschuss. He found the greater part of the walls covered with ice, and many pillars and pyramids of ice on the floor. The cold was moderate, and was said to be much the same in summer and winter. Patrin has given a fuller description of the same cavern in the Journalde Physique.[158] The lead-mine is in limestone rock, containing a third part of clay. The entrance to the glaciere was still difficult at the time of his visit, and it was necessary to use a rope, and also to cut steps, for the descent was made along a ridge of ice with almost perpendicular sides. The spectacle presented by the decoration of the roof was remarkably beautiful, long festoons and tufts of ice hanging down, light and brilliant as silver gauze: this ice was supposed to be formed from the abundant vapours of the beginning of winter, and resembled glass blown to the utmost tenuity. It was crystallised, too, in a wonderful manner. Patrin found long bundles of hexahedral tubes, the walls of which were formed of transverse needles: the diameter of these tubes was from two to six lines only, but at the lower extremities they opened out into hollow six-sided pyramids, more than an inch in diameter, so that the festoons, sometimes as large round as a man, presented terminal tufts of some feet in diameter, which glittered like diamonds under the influence of the torches. Towards the farther end of the fissure, stalactites of solid ice were found, displaying all the forms and more than all the beauty of limestone stalactites. The other instance mentioned by Georgi occurred in the mines of Serentvi, where two of the levels yielded perennial ice, and were thence (Georgi says) called Ledenoi. A spring of water flowed from the rock at a depth of thirty fathoms below the surface, and was promptly frozen into a coating of ice a foot thick. Patrin[159] visited Serentvi, but he did not observe any ice in the mines. He believed the rock to be very ancient lava.

Reich[160] mentions a cavern on Mount Sorano which contains ice, quoting Kircher;[161] but he seems to have misinterpreted his author's Latin.[162] He also refers to the existence of ice in the mines of Herrengrund in Hungary, and Dannemora in Sweden. Kircher, who has the credit of having been the first to call attention to the increase of temperature in the earth, made full enquiries into the temperature of the mines at Herrengrund, but he was not informed of the existence of ice.[163]; Townson visited these mines in the course of his travels in Hungary, and neither does he make any mention of ice in connection with them. He describes them as lying south of Teplitz, in a limestone district, with sandstone in the more immediate neighbourhood. The mines themselves (copper mines) are in a kind of mica-schist, which the people call granite. The superintendent of mines informed Reich that one of the shafts is called the ice-mine, from the fact that when the workmen attempted to drive a gallery from south to north, they came upon ice filling up the interstices of the Haldenstein, within five fathoms of the commencement of the gallery. The temperature was so low, and the expense caused by the frozen mass so great, that the working was stopped.

The iron mines of Dannemora, eleven leagues from Upsal, contain a large quantity of ice, according to a manuscript account by Mr. Over-assessor-of-the-board-of-mines Winkler:[164] Jars, however, in his Voyages Metallurgiques,[165] gives a full description of them without mentioning the existence of ice. He states that ice is found in the mines of Nordmarck, three leagues from Philipstadt in Wermeland, a province of Sweden: these mines are merely numerous shafts sunk in the earth, reaching to the bottom of the vein of ore, so that they are fully exposed to the light, and yet the walls of the shafts become covered with ice at the end of winter, which remains there till the middle of September. Jars believed that, if it were not for the heat caused by blasting, and by the presence of the workmen, the ice would be perennial. Humboldt[166] speaks of the ice in these mines and on the Sauberg. Reich states that ice is found in the mill-stone quarry of Nieder-Mendig, quoting Karsten's Archiv fuer Bergbau.[167] The ice is found in the hottest days of summer, although the interior of the quarry is connected with the outer air by many side shafts. The porous nature of the stone is assigned as the cause of the phenomenon. Daubeny (On Volcanoes) describes the remarkable basaltic deposits at Niedermennig—as he spells it—but says nothing of the existence of ice.

Daubuisson[168] speaks of a Schneegrube, on a summit of the Riesengebirge, in Silesia, 4,000 feet above the sea; but such holes are common enough at that elevation, and I have seen two or three remarkable instances on the Jura, within the compass of one day's walk. Voigt[169] describes an Eisgrube in the Rhoengebirge, on the Ringmauer, the highest point of the Tagstein, where abundant ice is found in summer under irregular masses of columnar basalt. Reich had received from a forest-inspector an account of an ice-hole in this neighbourhood, called Umpfen, which is apparently not the same as that mentioned by Voigt.

In the Saxon Erzgebirge there are three points remarkable for their low temperature,[170] in addition to the mines on the Sauberg mentioned above. These are the Heinrichssohle, in the Stockwerk at Altenberg, where the mean of two years' observations gives the temperature 0 deg..54 F. lower at a depth of 400 feet than at the surface; the adit of Henneberg, on the Ingelbach, near Johanngeorgenstadt, where the temperature was again 0 deg..54 F. lower than in shafts some hundred feet higher; and the Weiss Adler adit, on the left declivity of the valley of the Schwarzwasser, above the Antonshuette. It would appear that there are local causes which affect the temperature in the Erzgebirge, for Reich found that in several places the mean temperature of the soil was higher than that of the air: for instance—

Soil. Air. Height above the sea.

Altenberg ... 42.732 deg. Fahr. 41.27 deg. 2,450 feet Markus Roehling ... 43.542 deg. " 41.832 deg. 1,870" Johanngeorgenstadt. 43.115 deg. " 41.09 deg. 2,460"

The temperature at Markus Roehling is peculiarly anomalous, considering the elevation of the surface above the sea.

There is said to be an ice-cave in Nassau, but I have been unable to obtain any account of it, unless it be the same as the ice-field mentioned on page 303.

There is a cave in the south-east of Hungary[171] which presents the same features as several of the glacieres I have visited. It is called the Ice-hole of Scherisciora, and is described as lying in the Jura-kalk, at a distance of 2-1/2 hours north-east from the forest-house of Distidiul. The approach is by ladders, down a pit 30 fathoms wide and 24 deep; and when the bottom of this pit is reached, an entrance is found to the cave in the north wall, in the neighbourhood of which is congealed snow which shortly becomes ice. The floor of the first chamber is composed of glacier-ice, separated from the side walls by a cleft from 1 to 3 feet wide, where it shows a depth of from 4 to 6 feet; it is as smooth as glass, and about 6 fathoms from the entrance a cone of ice stands upon it, 8 or 9 feet high. Both the floor and the cone are at once seen to be transformed remains of ancient masses of snow, and are of a dirty yellow colour.

At the back of this chamber, a narrow passage opens towards the interior of the mountain, and winds steeply down with a height of 4 feet, and a length of a few fathoms, till a magnificent dome is reached, on the beauties of which Herr Peters becomes eloquent. The floor is so smooth that crimpons are necessary, and stalagmites and stalactites of ice are found in rich profusion, the latter being generally formed on small limestone stalactites, while the former have no such nucleus.

There is another opening near the original entrance to the cave, a sort of fissure covered with elegant forms of ice, leading to a steep shaft. The imperial forester of Topfanalva was bold enough to let himself down the slope of ice which formed the edge of the shaft, on a rope ladder 60 feet long, notwithstanding the difficulty of grasping the iron steps which of course lay pressed on to the ice; but when he had descended about 30 feet, the shaft became perpendicular, and stones thrown in showed a very considerable depth. There appeared to be no sound of water in the abyss below.

Both entrances, that to the shaft as well as that to the second chamber, were ornamented with delicate ice crystals, which occurred both on the limestone stalactites and on the walls, and presented almost the appearance of plants of cauliflower. The ice-floor of the first chamber is described as consisting of a 'coarse-grained' material.

In the south-east of Servia, on the western slope of Mount Rtagn, is a pit 20 feet in diameter, and 40 or 50 feet deep, the bottom of which is reached by a succession of trunks of trees with the branches lopped off, a sort of ladder called stouba by the natives.[172] The peasants assert that the snow and ice disappear from this pit in September, and do not reappear before June. The Swiss peasants have never yet got so far as to say that the snow in their pits disappears in winter and returns in summer. Boue[173] found the temperature of the bottom of the pit to be 28 deg..4 F., while that of the air outside was 76 deg. F. The same writer[174] mentions a source in a mill-stone quarry in Bosnia which is frozen till the end of June.

FOOTNOTES:

[Footnote 122: Several of these caves are referred to by Reich, Beobachtungen ueber die Temperatur des Gesteins in verschiedenen Tiefen in den Gruben des Saechsischen Erzgebirges; Freiberg, 1834.]

[Footnote 123: Naturwunder des Oesterr. Kaiserthums, iii. 40.]

[Footnote 124: Mittheil. des Oesterr. Alpen-Vereins, ii. 441. I am indebted to G.C. Churchill, Esq., one of the authors of the well-known book on the Dolomite Mountains, for my knowledge of the existence of this cave, and of the Kolowrathoehle.]

[Footnote 125: Beschreibung merkwuerdiger Hoehlen, ii. 283.]

[Footnote 126: Geognostische Reschreibung des bayerischen Alpengebirges; Gotha, 1861.]

[Footnote 127: These constitute the upper bone bed and Dachstein limestone beds of the uppermost part of the Trias formation.]

[Footnote 128: Hereynia Curiosa, cap. v. The same account is given in Behren's Natural History of the Harz Forest, of which an English translation was published in 1730.]

[Footnote 129: See also Muncke, Handbuch der Naturlehre, iii. 277; Heidelberg, 1830.]

[Footnote 130: See page 58. The more modern spelling is frais-puits.]

[Footnote 131: liv. 292.]

[Footnote 132: Described by Schaller, Leitmeritzer Kreis, p. 271, and by Sommer, in the same publication, p. 331. I have not been able to procure this book.]

[Footnote 133: Boehmens Topogr., i. 339. This reference is given by Professor Pleischl.]

[Footnote 134: Annalen, lxxxi. 579.]

[Footnote 135: I was told, in 1864, by a chamois-hunter of Les Plans, a valley two hours above Bex, that some years before he was cutting a wood-road through the forest early in September, when, at a depth of 6 inches below the surface, he found the ground frozen hard. We visited the place together, but could find no ice. The whole ground was composed of a mass of loose round stones, with a covering of earth and moss, and the air in the interstices was peculiarly cold and dry.]

[Footnote 136: Beobachtungen, &c. (see note on p. 258), 181.]

[Footnote 137: Reich found the temperature of the ice to be 31.982 deg. F., that of the air in the immediate vicinity 34.025 deg., and the rock, at a little distance, 32.765 deg..]

[Footnote 138: iii. 150.]

[Footnote 139: See many careful descriptions of these caves in the Annales de Chimie; also, an account by Professor Ansted, in his Science, Scenery, and Art, p. 29. M. Chaptal (Ann. de Chimie, iv. 34) found the lowest temperature of the currents of cold air to be 36.5 F.; but M. Girou de Buzareingues (Ann. de Chimie et de Phys., xlv. 362) found that with a strong north wind, the temperature of the external air being 55.4 F., the coldest current gave 35.6 F.; with less external wind, still blowing from the north, the external air lost half a degree centigrade of heat, while the current in the cave rose to 38.75 F. The cellars in which the famous cheese of Roquefort is ripened are not subterranean, but are buildings joined on to the rock at the mouths of the fissures whence the currents proceed. They are so valuable, that one, which cost 12,000 francs in construction, sold for 215,000 francs. The cheese of this district has had a great reputation from very early times. Pliny (Hist. Nat. xi. 97) mentions, with commendation, the cheeses of Lesura (M. Lozere or Losere) and Gabalum (Gevaudan, Javoux). The idolaters of Gevaudan offered cheeses to demons by throwing them into a lake on the Mons Helanus (Laz des Helles?) and it was not till the year 550 that S. Hilary, Bishop of Mende, succeeded in putting a stop to this practice.]

[Footnote 140: It would seem from his own account of the Sauberg, and from the description given above of the presence of ice among the rocky debris, as well as from the account on this page of ice in Virginia, that a formation of loose stones is favourable to the existence of a low degree of temperature. See also the note on p. 263, with respect to the loose stones near Les Plans. Forchhammer found, on the Faroe Islands, that springs which rise from loose stones are invariably colder than those which proceed from more solid rock at the same elevation, as indeed might have been expected.]

[Footnote 141: xvii. 337. The account is taken from a Dutch journal.]

[Footnote 142: xix. p. 124.]

[Footnote 143: October 11, 1829.]

[Footnote 144: viii. 254.]

[Footnote 145: Pp. 174-6.]

[Footnote 146: Thermometer about 85 deg. F.]

[Footnote 147: v. 154.]

[Footnote 148: iv. 300.]

[Footnote 149: Die erloeschenen Vulkane in der Eifel, S. 59.]

[Footnote 150: Dr. Gmelin, of Tubingen, detected the presence of ammonia both in clinkstone lava and in columnar basalt (American Journal of Science, iv. 371).]

[Footnote 151: Geology and Extinct Volcanoes of Central France, p. 60 (second edition).]

[Footnote 152: Mr. William Longman has informed me that some years ago he had ice given him in summer, when he was on a visit to the inspector of mines at Pont Gibaud, and he was told that it was formed in a neighbouring cavern during the hot season.]

[Footnote 153: Original edition of 1830, i. 369.]

[Footnote 154: See Professor Tyndall's Glaciers of the Alps, for an account of glacier-tables, sand-cones, &c. Anyone who has walked on a glacier will have noticed the little pits which any small black substance, whether a stone or a dead insect, sinks for itself in the ice.]

[Footnote 155: Gilbert, Annalen, lxix. 143.]

[Footnote 156: According to the latest accounts I have been able to obtain, a temperature of 29.75 deg. F. had already been reached some years ago; the temperature, a few feet from the surface, being 14 deg. below freezing. The soil here only thaws to a depth of 3 feet in the hottest summer. Sir R. Murchison wrote to Russia, in February last, for further information regarding this well.

Since I wrote this, Sir Roderick Murchison has applied to the Secretary of the Imperial Academy of St. Petersburg for further information respecting the investigations at Jakutsk. The Secretary gives a reference to Middendorff's Sibirische Reise, Bd. iv. Th. i., 3te Lieferung, Klima, 1861. I have only been able to find the edition of 1848-51; but in that edition, under the heading Meteorologische Beobachtungen, elaborate tables of the meteorological condition of Jakutsk are given (i. 28-49). Also, under the heading Geothermische Beobachtungen, very careful information respecting the frozen earth will be found (i. 157, &c., and 178, &c.). The point at which a temperature of 32 deg. will be attained, is reckoned variously at from 600 to 1,000 feet below the surface.]

[Footnote 157: Reise im Russischen Reich_, i. 359; St. Petersburg, 1772.]

[Footnote 158: xxxviii. 231 (an. 1791), in an article called _Notice mineral, de la Daourie]

[Footnote 159: L.c., p. 236.]

[Footnote 160: Beobachtungen, &c., 194.]

[Footnote 161: Mundus Subterraneus, i. 220 (i. 239, in the edition of 1678).]

[Footnote 162: 'Vidi ego in Monte Sorano cryptam veluti glacie incrustatam, ingentibus in fornice hinc inde stiriis dependentibus, e quibus vicini mentis accolae pocula aestivo tempore conficiunt, aquae vinoque quae iis infunduntur refrigerandis aptissima, extremo rigore in summas bibentium delicias commutato.']

[Footnote 163: Both here and at Schemnitz, Kircher made particular enquiries on a subject of which scientific men have altogether lost sight. At Schemnitz he asked the superintendent, an comparcant Daemunculi vel pygmaei in fodinis?—respondit affirmative, et narrat plura exempla; and at Herrengrund, utrum appareant Daemunculi seu pygmaei?—respondit tales visos fuisse, et auditos pluries. (Edition of 1678, ii. 203, 205.)]

[Footnote 164: Reich, 199.]

[Footnote 165: i. 108 (Lyon, 1794).]

[Footnote 166: Ueber die unterirdischen Gasarten, 101.]

[Footnote 167: xvii. 386.]

[Footnote 168: Mem. sur les Basaltes de la Saxe, p. 147.]

[Footnote 169: Mineralog. Reisen, ii. 123.]

[Footnote 170: Reich, 200, 201; Bischof, Physical Researches on the Internal Heat of the Globe, 46, 47.]

[Footnote 171: Peters, Geologische und mineralogische Studien aus dem sudoestlichen Ungarn, in the Sitzungsberichte der kais. Ak. in Wien, B. xliii., 1te Abth., S. 435. See also pages 394 and 418 of the same volume (year 1861).]

[Footnote 172: Such ladders are in ordinary use in the Jura.]

[Footnote 173: Turquie d'Europe, i. 132 (he quotes himself as i. 180, in the Sitzungsb, der k. Ak. in Wien, xlix. l. 324).]

[Footnote 174: L.c., p, 521.]

* * * * *



CHAPTER XVII.

HISTORY OF THEORIES RESPECTING THE CAUSES OF SUBTERRANEAN ICE.

The only glaciere which is in any sense historical, is that near Besancon; and a brief account of the different theories which have been advanced in explanation of the phenomena presented by it, will include almost all that has been written on ice-caves.

The first mention I have found of this cave is contained in an old history of the Franche Comte of Burgundy, published at Dole in 1592, to which reference has been already made. Gollut, the author, speaks more than once of a glaciere in his topographical descriptions, and in a short account of it he states that it lay near the village of Leugne, which I find marked in the Delphinal Atlas very near the site of the Chartreuse of Grace-Dieu; so that there can be no doubt that his glaciere was the same with that which now exists. His theory was, that the dense covering of trees and shrubs protected the soil and the surface-water from the rays of the sun, and so the cold which was stored up in the cave was enabled to withstand the attacks of the heat of summer.[175] In the case of many of the glacieres, there can be no doubt that this idea of winter cold being so preserved, by natural means, as to resist the encroachments of the hotter seasons, is the true explanation of the phenomenon of underground ice.

The next account of this glaciere is found in the History of the Royal Academy of Sciences (French), under the year 1686,[176] but no theory is there suggested. The writer of the account states that in his time the floor of the cave was covered with ice, and that ice hung from the roof in festoons. In winter the cave was full of thick vapours, and a stream of water ran through it. The ice had for long been less abundant than in former times, in consequence of the felling of some trees which had stood near the entrance.

The Academy received in the same year another letter on this subject, confirming the previous account, and adding some particulars. From this it would seem that people flocked from all sides to the glaciere with waggons and mules, and conveyed the ice through the various parts of Burgundy, and to the camp of the Saone; not thereby diminishing the amount of ice, for one hot day produced as much as they could carry away in eight days. The ice seemed to be formed from a stream which ran through the cave and was frozen in the summer only. The writer of this second account saw vapours in the glaciere (the editor of the Histoire de l'Academie does not say at what season the visit to the cave took place), and was informed that this was an infallible sign of approaching rain; so much so, that the peasants were in the habit of determining the coming weather by the state of the grotto.

In 1712, M. Billerez, Professor of Anatomy and Botany in the University of Besancon, communicated to the Academy[177] an account of a visit made by him to this cave in September 1711. He found 3 feet of ice on the floor of the cave, in a state of incipient thaw, and three pyramids, from 15 to 20 feet high and 5 or 6 feet in diameter, which had been already considerably reduced in size by thaw. A vapour was beginning to pass out from the cave, at the highest part of the arch of entrance; a phenomenon which, he was told, continued through the winter, and announced or accompanied the departure of the ice: nevertheless, the cold was so great that he could not remain in the glaciere more than half an hour with any sort of comfort. The thermometer stood at 60 deg. outside the cave, and fell to 10 deg.[178] when placed inside; but thermometrical observations of that date were so vague as to be useless for present purposes. The ice appeared to be harder than the ordinary ice of rivers, less full of air-bubbles, and more difficult to melt.

M. Billerez enunciated a new theory to account for the phenomena presented by the cave. He observed that the earth in the immediate neighbourhood, and especially above the roof of the grotto, was full of a nitrous or ammoniac salt, and he accordingly suggested that this salt was disturbed by the heat of summer and mingled itself with the water which penetrated by means of fissures to the grotto, and so the cave was affected in the same way as the smaller vessel in the ordinary preparation of artificial ice. He had heard that some rivers in China freeze in summer from the same cause.[179]

In 1726, a further communication was made to the Academy by M. des Boz,[181] Royal Engineer, describing four visits which he had made to the grotto near Besancon at four different seasons of the year, viz., in May and November 1725, and in March and August 1726. In all cases he found the air in the cave colder than the external air,[182] and its variations in temperature corresponded with the external variations, the cold being greater in winter than in summer.

M. des Boz ascribed the existence of ice in the cave to natural causes. The opening being towards the north-east, and corresponding with a gorge in the hills opposite, running in the same direction, none but cold winds could reach the mouth of the grotto. Moreover, the soil above was so thickly covered with trees and brushwood, that the rays of the sun could not reach the earth, much less the rock below. Credible persons asserted that since some of the trees had been felled, there had not been so much ice in the cave.

In order to test the presence of salt, M. des Boz melted some of the ice, and evaporated the resulting water, but found no taste of salt in the matter which remained.[183] He denied the existence of the spring of water which previous accounts had mentioned, and believed that the water which formed the ice came solely from melted snow, and from the fissures of the rock.

In 1727, the Duc de Levi caused the whole of the ice to be removed from the cave, for the use of the army of the Saone, which he commanded. In 1743 the ice had formed again, and the grotto was subjected to a very careful investigation by M. de Cossigny, chief engineer of Besancon, in the months of August and October.[183] The thermometer he used had been presented to him by the Academy, and was very probably constructed by M. de Reaumur himself, for de Cossigny's account was sent through M. de Reaumur to the Academy, but still the observations made with it cannot be considered very trustworthy. On the 8th of August, at 7.30 A.M., the temperature in the cave was 1/2 deg. above the zero point of this thermometer, and at 11.30 A.M. it had risen to 1 deg. above zero. On the 17th of October, at 7 A.M., the thermometer stood at 1/2 deg., and at 4 P.M. it gave the same register.

M. de Cossigny found that the entrance to the cave was rather more than 150 feet above the Abbey of Grace-Dieu, and about half a league distant by the ordinary path. A great part of his account is occupied by contradictions of previous accounts, especially in the matter of dimensions,[184] The people of Besancon had urged him to stay only a short time in the cave, because of the sulphureous and nitrous exhalations, but he detected no symptoms of anything of that kind. The most curious thing which he saw was the soft earth which lay, and still lies, at the bottom of the long slope of ice by which the descent is made; and he subjected this to various chemical tests and processes, but could not find that it contained anything different from ordinary earth.[185]

When M. de Cossigny visited the cave, there were thirteen or fourteen columns of ice, from 6 to 8 feet high, and he was in consequence inclined to doubt the accuracy of the statement of M. Billerez, that in his time (1711) there were three columns only, from 15 to 20 feet high. But my own observation of the shape of the columns suggested that the largest of all was probably an amalgamation of several others; so that it is not unreasonable to suppose that after the Duc de Levi removed the large columns seen by M. Billerez, a number of smaller columns were formed on the old site, and that these had not become large enough to amalgamate in 1743.

Not satisfied with these visits of August and October, M. de Cossigny visited the cave in April 1745. He found the temperature at 5 A.M. to be exactly at the freezing point, and at noon it had risen 1 deg.. From this he concluded that the stories of the greater cold in the cave during the summer, as compared with the winter, were false.

In 1769, M. Prevost, of Geneva, visited the cave, as a young man; and in 1789, he wrote an account of his visit in the Journal de Geneve (March), which was afterwards inserted as an additional chapter in his book on Heat.[186] He believed that one or two hundred toises was the utmost that could be allowed for the height of the hill in which the glaciere lies,—a sufficiently vague approximation. He rejected the idea of salt as the cause of ice, and came to the conclusion that the cave was in fact nothing more than a good natural ice-house, being protected by dense trees, and a thick roof of rock, while its opening towards the north sheltered it from all warm winds. He accounted for the original presence of ice as follows:—In the winter, stalactites form at the edges of various fissures in the roof, and snow is drifted on to the floor of the cave by the north winds down the entrance-slope. When the warmer weather comes, the stalactites fall by their own weight, and, lying in the drifted and congealed snow, form nuclei round which the snow is still further congealed, and the water which results from the partial thaw of portions of the snow is also converted into ice. Thus, a larger collection of ice forms in winter than the heat of summer can destroy; and if none of it were removed, it might, in the course of years, almost fill the cave. At the time of his visit (August), M. Prevost found only one column, from 6 to 8 feet high.

In 1783 (August 6), M. Girod-Chantrans visited the Glaciere of Chaux (so called from a village near the glaciere, on the opposite side from the Abbey of Grace-Dieu), and his account of the visit appeared in the Journal des Mines[187] of Prairial, an iv., by which time the writer had become the Citizen Girod-Chantrans. He found a mass of stalactites of ice hanging from the roof, as if seeking to join themselves with corresponding stalagmites on the floor of the cave; the latter, five in number, being not more than 3 or 4 feet high, and standing on a thick sheet of ice. There was a sensible interval between this basement of ice and the rock and stones on which it reposed: it was, moreover, full of holes containing water, and the lower parts of the cave were unapproachable by reason of the large quantity of water which lay there. The thermometer stood at 35 deg..9 F. two feet above the floor, and at 78 deg. F. in the shade outside. M. Girod-Chantrans determined, from all he saw and heard, that the summer freezing and winter thaw were fables, and he believed that the cave was only an instance of Nature's providing the same sort of receptacle for ice as men provide in artificial ice-houses. He was fortunate enough to obtain by chance the notes of a neighbouring physician, who had made careful observations and experiments in the glaciere at various seasons of the year, and a precis of these notes forms the most valuable part of his account.

Dr. Oudot, the physician in question, found ten columns in January 1778, the largest of which was 5-1/2 feet high. The flooring of ice was nowhere more than 15 inches thick, and the parts of the rock which were not covered with ice were perfectly dry. The thermometer—M. Girod-Chantrans used Reaumur, so I suppose that he gives Dr. Oudot's observations in degrees of Reaumur, though some of the results of that supposition appear to be anomalous—gave 22 deg. F. within the cave, and 21 deg. F. outside.

In April of the same year, the large column had increased in height to the extent of 13 inches; and the floor of ice on which it stood was 1-1/2 inch thicker, and extended over a larger area than before; the thermometer stood at 36 deg..5 F. and 52 deg. F. respectively in the same positions as in the former case. In July, the large column had lost 6 inches of its height, and the thermometer gave 38 deg..75 F. and 74 deg..75 F.

In October, the large column was only 3 feet high, and many of the others had disappeared, while their pedestal had become much thinner than it had been in the preceding months. There was also a considerable amount of mud in the cave, brought down apparently by the heavy rains of autumn. The thermometer gave 37 deg..6 F. and 63 deg..5 F.

On the 8th of January, 1779, there were nine columns of very beautiful ice, and one of these, as before, was larger than the rest, being 5 feet high and 10 feet in circumference. The temperatures were 21 deg. F. and 16 deg..15 F. in the cave and in the open air respectively.

Tradition related that, before the removal of the ice in 1727, one of the columns reached the roof, (Prevost calculated the limits of the height of the cave at 90 and 60 feet,) and this suggested to Dr. Oudot the idea of placing stakes of wood in the heads of the columns he found in the cave, in the hope that ice would thus collect in greater quantities under the fissures of the roof. Accordingly, he made holes in three of the columns, and established stakes 4, 5, and 10 feet high, returning on the 22nd of February, after an interval of six weeks, to observe the result of his experiment. He found the two shorter stakes completely masked with ice, forming columns a foot in diameter; and the longest stake, though not entirely concealed by the ice which had collected upon it, was crowned with a beautiful capital of perfectly transparent ice. The columns which had no stakes fixed upon them had also increased somewhat in size, but not nearly in the same proportion as those which were the subject of Dr. Oudot's experiment. The thermometer on this day gave 29 deg..5 F. and 59 deg. F. as the temperatures.

It may be remembered that I found one very beautiful column, far higher than any of those mentioned by Dr. Oudot, and higher than those which M. Billerez saw, formed upon the trunk and branches of a fir-tree. I have now no doubt that the peculiar shape of another—the largest of the three columns which were in the cave at the time of my visit—is due to the fact of its being a collection of several smaller columns, which have in course of time flowed into one as they increased separately in bulk, and that its height has been augmented by a device similar to that adopted by Dr. Oudot. The two magnificent capitals which this column possessed, as well as the numerous smaller capitals which sprang from its sides, will thus be completely accounted for.

One more account may be mentioned, before I proceed to the theory which has found most favour in Switzerland of late years. M. Cadet published some Conjectures on the formation of the ice in this cavern, in the Annales de Chimie, Nivose, an XI.[188] He saw the cave in the end of September 1791, and found very little ice—not a third of what there had been a month before, according to the account of his guide. The limonadier of a public garden in Besancon informed him that the people of that town resorted to the glaciere for ice when the supplies of the artificial ice-houses failed, and that they chose a hot day for this purpose, because on such days there was more ice in the cave. Ten chars would have been sufficient to remove all the ice M. Cadet found, and the air inside the cave seemed to be not colder than the external air; but, nevertheless, M. Cadet believed the old story of the greater abundance of ice in summer than in winter, and he attempted to account for the phenomenon.

The ground above and near the cave is covered with beech and chestnut trees, and thus is protected from the rays of the sun. The leaves of these trees give forth abundant moisture, which has been pumped up from their roots; and as this moisture passes from the liquid to the gaseous state, it absorbs a large quantity of caloric. Thus, throughout the summer, the atmosphere is incessantly refrigerated by the evaporation produced by the trees round the cave; whereas in winter no such process goes on, and the cave assumes a moderate temperature, such as is usually found in ordinary caves. Unfortunately for M. Cadet's theory, the facts are not in accordance with his imaginary data, nor yet with his conclusions. He adds, on the authority of one of his friends, that the intendant of the province, M. de Vanolles, wishing to preserve a larger amount of ice in the cave, built up the entrance with a wall 20 feet high, in which a small door was made, and the keys were left in the hands of the authorities of the neighbouring village, with orders that no ice should be removed. The effect of this was, that the ice diminished considerably, and they were obliged to pull down the wall again. M. Cadet saw the remains of the wall, and the story was confirmed by the Brothers of Grace-Dieu. It would be very interesting to know at what season this wall was built, and when it was pulled down. If my ideas on the subject of ice-caves are correct, it would be absolutely fatal to shut out the heavy cold air of winter from the grotto.

In 1822, M.A. Pictet, of Geneva, took up the question of natural glacieres, and read a paper before the Helvetic Society of Natural Sciences,[189] describing his visits to the caves of the Brezon and the Valley of Reposoir. In order to explain the phenomena presented by those caves, M. Pictet adopted De Saussure's theory of the principle of caves-froides, rendering it somewhat more precise, and extending it to meet the case of ice-caves. It is well known that, in many parts of the world, cold currents are found to blow from the interstices of rocks; and these are utilised by neighbouring proprietors, who build sheds over the fissures, and so secure a cool place for keeping meat, &c. Examples of such currents are met with near Rome (in the Monte Testaceo), at Lugano, Lucerne (the caves of Hergiswyl), and in various other districts. It is found that the hotter the day, the stronger is the current of cold air; in winter the direction of the current is changed, and it blows into the rock instead of out from it.[190] De Saussure's theory, as developed by M. Pictet, was no doubt satisfactory, so far as it was used to account for the phenomenon of 'cold-caves,' but it seems to be insufficient as an explanation of the existence of large masses of subterranean ice; of which, by the way, De Saussure must have been entirely ignorant, for he makes no allusion to such ice, and the temperatures of the coldest of his caves were considerably above the freezing point.

Pictet represents the case of a cave with cold currents of air to be much the same as that of a mine with a vertical shaft, ending in a horizontal gallery of which one extremity is in communication with the open air, at a point much lower, of course, than the upper extremity of the shaft. The cave corresponds to the horizontal gallery, and the various fissures in the rock take the place of the vertical shaft, and communicate freely with the external air. In summer, the columns of air contained in these fissures assume nearly the temperature of the rock in which they rest, that is to say, the mean temperature of the district, and therefore they are heavier than the corresponding external columns of air which terminate at the mouth of the cave; for the atmosphere in summer is very much above the mean temperature of the soil, or of the interior of the earth at moderate depths. The consequence is, that the heavy cool air descends from the fissures, and streams out into the cave, appearing as a cold current; and the hotter the day is—that is, the lighter the columns of external air—the more violent will be the disturbance of equilibrium, and therefore the more palpable the cold current. Naturally, in this last case, the air which enters by the upper orifices of the fissures is more heated, to begin with, than on cooler days; but external heat so very slightly affects the deeper parts of the fissures, that the columns of air thus introduced are speedily impressed with the mean temperature of the district. In winter, the external columns of air are as much heavier than the columns in the fissures as they are lighter in summer; and so cold currents of air blow from the cave into the fissures, though such currents are not of course colder than the external air. Thus the mean temperature of the cave is much lower than that of the rock in which it occurs; for the temperature of the currents varies from the mean temperature of the rock to the winter temperature of the external atmosphere.

The descending columns of warmer air, in summer, must to some extent raise the temperature of the fissures above that which they would otherwise possess, that is, above the mean temperature of the place; but that may be considered to be counteracted by the corresponding lowering of the temperature of the fissures by the introduction of cold air from the cave in winter. By a similar reasoning, it will be seen that for some time after the spring change of direction in the currents takes place, the temperature of the cave will be less than would have been expected from a calculation founded on the true mean temperature of the rock through which the fissures pass. This, together with the fact of the porous nature of the rock in which most of the curious caves in the world occur, which allows a considerable amount of moisture to collect on all surfaces, and thereby induces a depression of temperature by evaporation, may be held to explain the presence of a greater amount of cold than might otherwise have been fairly reckoned upon in ice-caves.

The idea of cold produced by evaporation Pictet took up warmly, believing that when promoted by rapid currents of air it would produce ice in the summer months; and he thus explained what he understood to be the phenomena of glacieres. But it will have been seen, from the account of the caves I have visited, that the glacieres are more or less in a state of thaw in the summer; and M. Thury's observations in the winter prove conclusively that they are then in a state of utter frost, so that the old belief with respect to the season at which the ice is formed may be supposed to have been exploded. The facts recorded by Mr. Scrope[191] would appear to depend upon the peculiar nature of rocks of volcanic formation; and I am inclined to think there is very little in common between such instances as he mentions and the large caves filled with ice which are to be found in the primary or secondary limestone.

One of De Saussure's experiments, in the course of his investigation of the phenomena and causes of cold currents in caves, is worth recalling. He passed a current of air through a glass tube an inch in diameter, filled with moistened stones, and by that means succeeded in reducing the temperature of the current from 18 deg. C. to 15 deg. C.; and when the refrigerated current was directed against a wet-bulb thermometer, it fell to 14 deg. C., thus showing a loss of 7 deg..2 F. of heat. No one can see much of limestone caverns without discovering that the surfaces over which any currents there may be are constrained to pass, present an abundance of moisture to refrigerate the currents; and it is not unreasonable to suppose that the large number of evaporating surfaces, which currents passing through heaps of debris—such as the basaltic stones described on page 261—come in contact with, are the main cause of the specially low temperature observed under such circumstances.

Pictet's theory, however, did not convince all those into whose hands his paper fell, and M.J. Deluc wrote against it in the Annales de Chimie et de Physique of the same year, 1822.[192] Deluc had not seen any glaciere, but he was enabled to decide against the cold-current theory by a perusal of Pictet's own details, and of one of the accounts of the cave near Besancon. He objected, that in many cases the ice is found to melt in summer, instead of forming then; and also, that in the Glaciere of S. Georges, which Pictet had described, there was no current whatever. Further, in all the cases of cold currents investigated or mentioned by De Saussure, the presence of summer ice was never even hinted at, and the lowest temperatures observed by him were considerably above the freezing point. I may add, from my own experience, that on the only occasions on which I found a decided current in a glaciere—viz., in the Glaciere of Monthezy, and that of Chappet-sur-Villaz,—there was marked thaw in connection with the current. In the latter case, the channel from which the current came was filled with water; and in the former, water stood on the surface of the ice.

The view which Deluc adopted was one which I have myself independently formed; and he would probably have written with more force if he had been acquainted with various small details relating to the position and surroundings of many of the caves. The heavy cold air of winter sinks down into the glacieres, and the lighter warm air of summer cannot on ordinary principles of gravitation dislodge it, so that heat is very slowly spread in the caves; and even when some amount of heat does reach the ice, the latter melts but slowly, for ice absorbs 60 deg. C. of heat in melting; and thus, when ice is once formed, it becomes a material guarantee for the permanence of cold in the cave.

For this explanation to hold good, it is necessary that the level at which the ice is found should be below the level of the entrance to the cave; otherwise the mere weight of the cold air would cause it to leave its prison as soon as the spring warmth arrived. In every single case that has come under my observation, this condition has been emphatically fulfilled. It is necessary, also, that the cave should be protected from direct radiation, as the gravitation of cold air has nothing to do with resistance to that powerful means of introducing heat. This condition, also, is fulfilled by nature in all the glacieres I have visited, excepting that of S. Georges; and there art has replaced the protection formerly afforded by the thick trees which grew over the hole of entrance. The effect of the second hole in the roof of this glaciere is to destroy all the ice which is within range of the sun. A third and very necessary condition is, that the wind should not be allowed access to the cave; for if it were, it would infallibly bring in heated air, in spite of the specific weight of the cold air stored within. It will be understood from my descriptions of such glacieres as that of the Grand Anu, of Monthezy, and the Lower Glaciere of the Pre de S. Livres, how completely sheltered from all winds the entrances to those caves are. There can be no doubt, too, that the large surfaces which are available for evaporation have much to do with maintaining a somewhat lower temperature than the mean temperature of the place where the cave occurs. This had been noticed so long ago as Kircher's time; for among the answers which his questions received from the miners of Herrengrund, we find it stated that, so long as mines are dry, the deeper they are the hotter; but if they have water, they are less warm, however deep. From the mines of Schemnitz he was informed that, so long as the free passage of air was not hindered, the mines remained temperate; in other cases they were very warm. Another great advantage which some glacieres possess must be borne in mind, namely, the collection of snow at the bottom of the pit in which the entrance lies. This snow absorbs, in the course of melting, all heat which strikes down by radiation or is driven down by accidental turns of the wind; and the snow-water thus forced into the cave will, at any rate, not seriously injure the ice. It is worthy of notice that the two caves which possess the greatest depth of ice, so far as I have been able to fathom it, are precisely those which have the greatest deposit of snow; and the ice in a third cave, that of Monthezy, which has likewise a large amount of snow in the entrance-pit, presents the appearance of very considerable depth. The Schafloch, it is true, which contains an immense bulk of ice, has no snow; but its elevation is great, as compared with that of some of the caves, and therefore the mean temperature of the rock in which it occurs is less unfavourable to the existence of ice.

I believe that the true explanation of the curious phenomena presented by these caves in general, is to be found in Deluc's theory, fortified by such facts as those which I have now stated. The mean temperature of the rock at Besancon, where the elevation above the sea is comparatively so small, renders the temptation to suggest some chemical cause very strong.

The question of ice in summer where thaw prevails in winter, may fairly be considered to have been eliminated from the discussion of such caves as I have seen, in spite of the persistent assertions of some of the peasantry. The observations, however, in caverns in volcanic formations, and in basaltic debris, are so circumstantial that it is impossible to reject them; and in such cases a theory similar to that enunciated by Mr. Scrope[193] seems to be the only one in any way satisfactory, though I have not heard of such marvellous results being produced elsewhere by evaporation. One observer, for instance, of the cavern near the village of Both, in the Eiffel, found a thickness of 3 feet of ice; and in that case it was melting in summer, instead of forming. In some cases it has been suggested that the length of time required for external heat or cold to penetrate through the earth and rock which lie above the caves is sufficient to account for the phenomenon of summer frost and winter thaw. Thus, it is said, the thickness of the superincumbent bed may be such that the heat of summer only gets through to the cave at Christmas, and then produces thaw, while in like manner the greatest cold will reach the cave in mid-summer. But there is a fatal objection to this idea in the fact that the invariable stratum—i.e., the stratum beyond which the annual changes of external temperature are not felt—is reached about 60 feet below the surface in temperate latitudes,[194] while at the tropics such changes are not felt more than a foot below the surface. Humboldt calculated that in the latitude of central France the whole annual variation in temperature at a depth of 30 feet would not amount to more than one degree.[195]

FOOTNOTES:

[Footnote 174: As Gollut's phraseology is peculiar, it may be as well to reproduce his account of the cave:—'Je ne veux pas omettre toutefois (puisque je suis en ces eaux) de mettre en memoire la commodite que nature hat done a quelques delicats, puis qu'au fond d'un montagne de Leugne, la glace (glasse in the index), se treuve en este, pour le plaisir de ceux qui aimẽt a boire frais. Neanmoins dans ce tẽps cela se perd, no pour autre raison (ainsi que ie pense) que pour ce que lon hat depouille le dessus de la motagne d'une epoisse et aulte fustaie de bois, qui ne permettoit pas que les raions du soleil vinsent echauffer la terre et deseicher les distillations, que se couloiẽt iusques au plus bas et plus froid de la montagne: ou (par l'antiperistase) le froid s'epoississoit, et se reserroit, contre les chaleurs, entornantes et environnantes le long de l'este, toute la circonference exterieure du mont.'—Histoire, &c., p. 87.]

[Footnote 175: Hist. de l'Acad., t. ii., p. 2.]

[Footnote 176: Hist. de l'Acad., an 1712, p. 20.]

[Footnote 177: C'est a dire—M. Billerez explains—a 10 degres au-dessous du tres-grand froid. What the 60 deg. may be worth, I cannot say.]

[Footnote 178: Tournefort (Voyage du Levant, iii. 17) believed that the ammoniac salt, of which the earth was full in some districts near Erzeroum, had something to do with the persistence of snow on the ground there.]

[Footnote 179: Hist, de l'Acad., an 1726, p. 16.]

[Footnote 180: But see on this point the experience of M. Thury, in the Glaciere of S. Georges (Appendix).]

[Footnote 181: Sir Roderick Murchison's suggestion of the possible influence of salt in producing the phenomena of his ice-cave in Russia, did not, of course, proceed upon the supposition of salt actually mingling with water, but only of its increasing the evaporation of the air which came in contact with it.]

[Footnote 182: Mem. presentes a l'Academie par divers Scavans, i, 195.]

[Footnote 183: A long account was published in a history of Burgundy, printed at Dijon, in quarto, in 1737, which I have not been able to find. It was from the same source as the account in the Hist. of the Academy, in 1726.]

[Footnote 184: I took this earth to be a collection of the particles carried down the slope of ice by the heavy rains of the month preceding my visit. M. de Cossigny speaks of the abundant rains of July, his visit being in August.]

[Footnote 185: Recherches sur la Chaleur; Geneva and Paris, 1792.]

[Footnote 186: P. 65. Now called Annales des Mines.]

[Footnote 187: T. xlv. p. 160.]

[Footnote 188: Bibliotheque Universelle de Geneve, Premiere Serie, t. xx.]

[Footnote 189: See De Saussure's account of his numerous observations of such caves in the Voyage dans les Alpes, sections 1404-1415.]

[Footnote 190: P. 271.]

[Footnote 191: P. 271.]

[Footnote 192: xxi. 113.]

[Footnote 193: P. 271.]

[Footnote 194: Daubuisson estimated the depth in question at from 46 to 61 feet, while Kupffer put it at 77 feet.]

[Footnote 195: De Saussure found a variation of 2 deg..25 F. at a depth of 29.5 feet; but this was in a well, where the influence of the atmosphere was allowed to have effect. Naturally, the fissures which there may be in the rock surrounding a cave will increase the annual variation of temperature, by affording means of easier penetration to the heat and cold.

Sir K. Murchison's cavern in Russia would seem to be entirely sui generis.]

* * * * *



CHAPTER XVIII.

ON THE PRISMATIC STRUCTURE OF THE ICE IN GLACIERES.

It was natural to suppose that the prismatic structure which I found so very general in the glacieres was the result of some cause or causes coming into operation after the first formation of the ice. On this point M. Thury's visit to the Glaciere of S. Georges in the spring of 1852 affords valuable information, for at that time the coating of ice on the wall, evidently newly formed, did not present the structure areolaire which he had observed in his summer visit to the cave. He suggests that, since ice is less coherent at a temperature of 32 deg. F.—which is approximately the temperature of the ice-caves during several months of the year—than when exposed to a greater degree of cold, its molecules will then become free to assume a fresh system of arrangement.[196] On the other hand, Professor Faraday has found that ice formed under a temperature some degrees below the ordinary freezing point has a well-marked crystalline structure.[197] M. Thury suggests also, as a possibility, what I have found to be the case, by frequent observations, that the prismatic ice has greater power of resisting heat than ordinary ice; and on this supposition he accounts for the fact of hollow stalactites being found in the Cavern of S. Georges.[198] At the commencement of the hot season, the atmospheric temperature of the glacieres rises gradually; and when it has almost reached 32 deg. F., the prismatic change takes place in the ice, extending to a limited depth below the surface. The central parts of the stalactites retain their ordinary structure, and are after a time exposed to a general temperature rather above than below the freezing point; and thus they come to melt, the water escaping either by accidental fissures between some of the prisms, or by the extremity of the stalactite, or by some part of the surface which has chanced to escape the prismatic arrangement, and has itself melted under increased temperature.[199]

M. Hericart de Thury describes the peculiar structure of the ice which he found in the Glaciere of the Foire de Fondeurle.[200] He found that the crystallised portions were very distinctly marked, displaying for the most part a six-sided arrangement; and in the interior of a hollow stalactite he found numerous needles of ice perfectly crystallised, the crystals being some triangular and some six-sided. He was unable to detect any perfect pyramid.[201] I have already quoted Olafsen's observations on the polygonal lining which he saw on the surface of the ice in the Surtshellir. The French Encyclopaedia [202] relates that M. Hassenfratz saw ice served up at table at Chambery which broke into hexagonal prisms; and when he was shown the ice-houses where it was stored, he found considerable blocks of ice containing hexahedral prisms terminated by corresponding pyramids.

In vol. xv. (New Series) of the American Journal of Science,[203] an extract is given from a letter describing the 'Ice Spring' in the Rocky Mountains, which the mountaineers consider to be one of the curiosities of the great trail from the States to Oregon and California. It is situated in a low marshy 'swale' to the right of the Sweetwater river, and about forty miles from the South Pass. The ground is filled with springs; and about 18 inches below the turf lies a smooth and horizontal sheet of ice, which remains the year round, protected by the soil and grass above it. On July 12th, 1849, it was from 2 to 4 inches thick; but one of the guides stated that he had seen it a foot deep. It was perfectly clear, and disposed in hexagonal prisms, separating readily at the natural joints. The ice had a slightly saline taste,[204] the ground above it being impregnated with salt, and the water near tasting of sulphur. The upper surface of the stratum of ice was perfectly smooth.

In Poggendorff's Annalen (1841, Erganzsband, 517-19,—Boue, an old offender in that way, says 1842) there is an account of ice being found in the Westerwald, near the village of Frickhofen at the foot of the Dornburg, among basaltic debris about 500 feet above the sea.[205] Commencing at a depth of 2 feet below the surface, the ice reaches from 20 to 22 feet farther down, where the loose stones give place to dry sand. The ice is in thin layers on the stones, and is deposited in the form of clear and regular hexagonal crystals. The lateral extent through which this phenomenon obtains is from 40 to 50 feet each way, and is greater in winter than in summer. As in other cases that have been noticed in basaltic debris, the snow which falls upon the surface here is speedily melted. The Allgemeine Zeitung (1840, No. 309), from which the account in Poggendorff is taken, suggested that the melted snow-water which would thus run down among the interstices would readily freeze below the surface, while the heavy cold air of winter would be stored up at the lower levels, and the poor conducting powers of basaltic rock[206] would favour its permanence through the summer. The temperature of the cold current which was perceptible in the parts of the mass of debris where the ice existed was 1 deg. R. (34 deg..25 F.). Nothing but a few lichens grow on the surface of the debris.

These are, I think, all the references I have met with to the prismatic structure of subterranean ice. But there is an interesting account in Poggendorff 's Annalen,[207] by a private teacher in Jena, of the crystalline appearance of ice under slow thaw near that town. In the winter of 1840, the Saale was frozen, and the ice remained unbroken till the middle of January, when the thermometer rose suddenly, and the river in consequence overflowed the lower grounds, and carried large masses of ice on to the fields, where it was left when the water subsided. On the 20th of January the thermometer fell again, and remained below the freezing point till the 12th of February: some of the ice did not disappear till the following month.

When the ice had lain a short time, cracks appeared on the surface exposed to the sun, and spread like a network from the edges towards the centre of the surface. At first there was no regularity in the connection of these lines, and the several meshes were of very different sizes. After a time, the larger meshes split up into smaller, and the system of network was found to penetrate below the surface, the cracks deepening into furrows, which descended perpendicularly from the surface, and divided the ice into long thin rhomboidal pillars. The surface-end of some of these pillars was strongly marked with right lines parallel to one of the sides of the mesh, and it was found that there was a tendency in the ice to split down planes through these lines and parallel to the corresponding side-plane. Parallel to the original surface of the mass of ice, the pillars broke off evenly. The side-planes had a rounded, wrinkled appearance; and their mutual inclinations—as far as could be determined—were from 105 deg. to 115 deg., and from 66 deg. to 75 deg.. When these ice-pillars were examined by means of polarised light, they were found to possess a feeble double-refracting power.

The writer of the article in Poggendorff suggests a question which he was not sure how to answer:—Is this appearance in correspondence with the original formation of the ice, or does it only appear under slow thaw?

It is worthy of remark, that from the 1st to the 11th of February the thermometer was never higher than 22 deg..8 F., and during that time fell as low as 21 deg. below zero, i.e. 43 deg. below the freezing point.

Professor Tyndall has informed me that in the winters of 1849, 1850, 1851, he found the banks of a river in Germany loaded with massive layers of drift-ice, in a state of thaw, and was struck by the fact that every layer displayed the prismatic structure described above, the axes of the prisms being at right angles to the surfaces of freezing. It may be, he adds, that this structure is in the first place determined by the act of freezing, but it does not develop itself until the ice thaws.

M. Hassenfratz observed an appearance in ice on the Danube at Vienna[208] corresponding to that described at Jena. He gives no information as to the state of the weather or the temperature at the time, nor any of the circumstances under which the ice came under his notice. One of the masses of ice which he describes was crystallised in prisms of various numbers of sides: of these prisms the greater part were hexahedral and irregular. Another mass was composed of prisms in the form of truncated pyramids; and in another he found quadrilateral and octahedral prisms, the former splitting parallel to the faces, and also truncated pyramids with five and six sides. He adds, that he had frequently seen in the upper valleys tufts of ice growing, as it were, out of the ground, and striated externally, but had never succeeded in discovering any internal organisation, until one evening in a time of thaw, when he found by means of a microscope that the striated tufts of ice had assumed the same structure on a small scale as that which he had observed on the Danube.

A Frenchman who was present in the room in which the Chemical Section of the British Association met at Bath, and heard a paper which I read there on this prismatic structure, suggested that it was probably something akin to the rhomboidal form assumed by dried mud; and I have since been struck by the great resemblance to it, as far as the surface goes, which the pits of mud left by the coprolite-workers near Cambridge offer, of course on a very large scale. This led me to suppose that the intense dryness which would naturally be the result of the action of some weeks or months of great cold upon subterranean ice might be one of the causes of its assuming this form, and the observations at Jena would rather confirm than contradict this view: competent authorities, however, seem inclined to believe that warmth, and not cold, is the producing cause.[209]

Professor Tyndall found, in the course of his experiments on the discs and flowers produced in the interior of a mass of ice by sending a warm ray through the mass, that the pieces of ice were in some cases traversed by hazy surfaces of discontinuity, which divided the apparently continuous mass into irregular prismatic segments. The intersections of the bounding surfaces of these segments with the surface of the slab of ice formed a very irregular network of lines.[210] I am inclined, however, to think that the irregularity in these cases proved to be so much greater than that observed in the glacieres, that this interior prismatic subdivision must be referred to some different cause.

FOOTNOTES:

[Footnote 196: The continued extrication of latent heat by ice, as it is cooled a few degrees below 32 deg. F., appears to indicate a molecular change subsequent to the first freezing.—Phil. Trans., as quoted in the next note.]

[Footnote 197: See the paper 'On Liquid Diffusion as applied to Analysis,' by the Master of the Mint (Phil. Trans. 1861, p. 222).]

[Footnote 198: Compare the description of one of the hollow stalagmites I explored in the Schafloch, p. 145.]

[Footnote 199: Professor Tyndall has pointed out that, owing to the want of perfect homogeneity, some parts of a block of ice exposed to a temperature of 32 deg. F. will melt, while others remain solid (Phil. Trans. 1858, p. 214). He also arrived at the conclusion (p. 219) that heat could be conducted through the substance of a mass, and melt portions of the interior, without visible prejudice to the solidity of the other parts of the mass.]

[Footnote 200: Journal des Mines, xxxiii. 157. See also an English translation of his account in the second volume of the Edinburgh Journal of Science.]

[Footnote 201: It is to be hoped that the accuracy of his scientific descriptions exceeds that of his topographical information; for he states that the glaciere is two leagues from Valence, whereas it cost me six hours' drive on a level road, and five and a half hours' walking and climbing, to reach it from that town.]

[Footnote 202: Branch Physique, article Glace]

[Footnote 203: P. 146 (an. 1853).]

[Footnote 204: Dr. Lister experimented on sea-water in December 1684 (Ph. Trans, xiv. 836), and found that though it took two nights to freeze, it was much harder when once frozen than common ice, lasting for three-quarters of an hour under a heat which melted 100 times its bulk of common ice at once. It was marked with oblong squares, and had a salt taste. Ice formed from water with an admixture of sulphuric acid is said to assume a crystalline appearance.]

[Footnote 205: See also a pamphlet entitled Das unterirdische Eisfeld bei der Dornburg am Suedlichen Fusse des Westerwaldes, by Thomae of Wiesbaden (32 pages, with a map of the district), published in 1841.]

[Footnote 206: But see page 262.]

[Footnote 207: lv. (an 1842), 472.]

[Footnote 208: Journal de Physique, xxvi. (an 1785), 34.]

[Footnote 209: In looking through some early volumes of the Philosophical Transactions, I found an 'Extract of a letter written by Mr. Muraltus of Zurich (September 1668), concerning the Icy and Chrystallin Mountains of Helvetia, called the Gletscher, English'd out of Latin' (Phil. Trans. iv. 982), which at first looked something like an assertion of the prismatic structure of ice on a large scale. The English version is as follows:—'The snow melted by the heat of the summer, other snow being faln within a little while after, and hardened into ice, which by little and little in a long tract of time depurating itself turns into a stone, not yielding in hardness and clearness to chrystall. Such stones closely joyned and compacted together compose a whole mountain, and that a very firm one; though in summer-time the country-people have observed it to burst asunder with great cracking, thunder-like.']

[Footnote 210: See the woodcut illustrating Professor Tyndall's remarks in the 148th volume of the Philosophical Transactions (1858, p. 214).]

* * * * *



CHAPTER XIX.

ON THE MEAN TEMPERATURE OF THE REGIONS IN WHICH THE GLACIERES OCCUR.

Many interesting experiments have for long been carried on with a view to determine the mean temperature at various depths below the surface of the earth. The construction of Artesian wells has afforded useful opportunities for increasing the amount of our knowledge on this subject; and the well at Pregny, near Geneva,[211] and the Monk Wearmouth coal-mines, as observed by Professor Phillips while a fresh shaft was being sunk,[212] have supplied most valuable facts. Without entering into any detail, which would be an unnecessary trouble, it may be stated generally, that, under ordinary circumstances, 1 deg. F. of temperature is gained for every 50 or 60 feet of vertical descent into the interior of the earth. I have only met with one account of an experiment made in a horizontal direction, and it is curious that the law of the increase of temperature then observed seemed to be very much the same as that determined by the mean of the vertical observations. Boussingault[213] found several horizontal adits in a precipitous face of porphyritic syenite among the mountains of Marmato. In one of these adits—a gallery called Cruzada, at an elevation of 1,460 metres—he found an increase of 1 deg. C. of mean temperature for every 33 metres of horizontal penetration, or, approximately, 1 deg. F. for 60 feet.[214]

Again, observations have been made, in various latitudes, of the decrease of temperature consequent upon gradual rising from the general surface of the earth; as, for instance, in the ascent of mountains. Speaking without any very great precision, but with sufficient accuracy for ordinary purposes, 1 deg. F. is lost with every 300 feet of ascent.[215] It is evident that this decrease will be less rapid where the slope of ascent is gradual, from such considerations as the angle at which the sun's rays strike the slope, and the larger amount of surface which is in contact with a stratum of atmosphere of any given thickness.

With these data, it is easy to arrive at some idea of the probable mean temperature of the rock containing several of the glacieres I have described. The elevation of some of them has not been determined with sufficient accuracy to make the results of any calculation trustworthy; but four cases may be taken where the elevation is known—namely, the Glacieres of S. Georges, S. Livres, Monthezy, and the Schafloch. If we take as a starting point the mean temperature of the town of Geneva, which has been determined at 49 deg..55 F., the elevation of that town being nearly 1,200 feet, we obtain the following approximate results for the mean temperature of the surface at the points in question:—

S. Georges .... 40 deg..22 Fahr. S. Livres (Lower) .... 38 deg..55" Schafloch .... 33 deg..88" Monthezy .... 41 deg..55"

The law of decrease of temperature enunciated by M. Thury gives a higher mean temperature for the surface of the earth in these places, as in the following table:—

S. Georges .... 41 deg..8 Fahr. S. Livres .... 40 deg..1" Schafloch .... 35 deg..6" Monthezy .... 42 deg..5"

If any certain information could be obtained of the elevation of the Abbey of Grace-Dieu, I am sure that a result more surprising than that in the case of the Glaciere of Monthezy would appear. The elevation of the floor of the church in the citadel of Besancon is 367.7 metres, and the plateau on the north side of the town of Baume-les-Dames is 531.9 metres. I am inclined to think, from the look of the country, that the latter possesses much the same elevation as the valley in which the Abbey lies; and in that case we should have comparatively a very high mean temperature for the surface in the neighbourhood where the glaciere occurs.

But if these are the mean temperatures of the surface, the natural temperatures of the caves themselves should be still higher, on account of the allowance to be made for increase of temperature with descent into the interior of the earth. This element will very materially affect our calculations in such a case as the lower part of the ice in the Glaciere of the Pre de S. Livres, and the strange suggestive beginning of a new ice-cave 190 feet below the surface, on the Montagne de l'Eau, near Annecy. In any open pit or cave, the ordinary atmospheric influences find such easy access, that the temperature cannot be expected to follow the law observed when perforations of small bore are made in the earth, as in the case of the preliminary boring before commencing to dig a well;[216] but the two glacieres mentioned above are so completely protected in their lowest parts, that they may be treated as if they were isolated from external influence of all ordinary kinds; and it may fairly be said that the mean temperature there ought to be considerably higher than at the surface.

It is not very likely that the results of the above calculations are strictly in accordance with what a careful series of observations on the spot might show. The distance between Geneva and the Glacieres of S. Georges and S. Livres is sufficiently small to make it probable that the reality is not very far different from the calculated temperature; but the other two caves are comparatively so far off, that the temperature and elevation of Geneva are not very safe data to build upon.

FOOTNOTES:

[Footnote 211: Bischof, Physical Researches, 189.]

[Footnote 212: Philosophical Magazine, v. 446 (1834).]

[Footnote 213: Annules de Chimie et de Physique, liii. 2-10. See also Bischof, 136.]

[Footnote 214: The English edition of Bischof affords here a proof of the danger of frequent changes from one scale to another. Bischof in the first instance rendered Boussingault into degrees Reaumur, and this was in turn reduced to degrees Fahrenheit; the result being that the authorised English edition of his book gives 2 deg..25 F. for 127.5 feet, which does not come within 10 feet of Boussingault's statement.]

[Footnote 215: M. Thury calculates a decrease of 1 deg. C. for every 174 metres between Geneva and S. Bernard, which is less than the decrease given in the text. He arrives at this conclusion by correcting the mean temperature of Geneva from 8 deg..9 C., the observed mean of eighteen years, to 9 deg..9 C., in consequence of supposed local causes, which unduly depress the temperature of Geneva. With the mean 8 deg..9 C. a result nearly in accordance with that of the text is obtained.]

[Footnote 216: Professor Phillips found, in the course of his investigations in the Monk Wearmouth mines, some hundreds of yards below the sea, that when a new face of rock was exposed, its temperature was considerably higher than that of the gallery or shaft in which it lay. In some cases the difference amounted to 9 and 10 degrees. The rock soon cooled down to an agreement with the surrounding temperature.]

* * * * *



APPENDIX.

M. Thury's observations during his winter visit to the Glaciere of S. Georges are so curious and valuable, that I give the principal results of them here.

It will be remembered that this glaciere consists of a roomy cave, 110 feet long and 60 feet high, with two orifices in the higher part of the roof, one of which is kept covered with the trunks of trees to shut out the direct radiation of the sun. A little thought suggested to M. Thury that the cold in the cave in mid-winter would most probably be greater than the external cold of the day, and less than that of the night; so that there should be a time in the later evening when a column of colder and heavier air would begin, to descend through the hole in the roof. To test the correctness of this supposition, he took up his abode in the cavern for the evening of the 10th January, 1858, with a lighted candle. The flame burned steadily for some time; but at 7.16 P.M. it began to flicker, and soon inclined downwards through an angle of about 45 deg.; and when M. Thury placed himself under the principal opening, the flame was forced into an almost horizontal position. At 8 P.M. the current of air had all but disappeared. This violent and temporary disturbance of equilibrium was a matter of much surprise to M. Thury; for he had naturally expected a quiet current downwards, continuing through the greater part of the night.

THE END